Principle of Parsimony
by Kuro49
Summary: Luther!AU. Stacker/Herc. It's Detective Stacker Pentecost's first day back on the job when he meets Hercules Hansen in a double homicide.


**Warnings: Major character deaths, also **awful things happen to Max**, and by awful, I mean Max dies in a pretty horrific manner. So read at your own discretion. If you have watched the pilot episode of Luther, you can probably guess who dies, but still.

THIS IS A TERRIBLE THING THAT HAPPENED WHEN I MAINLINED ALL THREE SEASONS OF LUTHER IN ONE SITTING. I AM SORRY.

XXX

**Principle of Parsimony**

XXX

The man's got red-rimmed eyes and hands that shake.

That's the first observation DCI Stacker Pentecost makes when he walks on to the crime scene. Mr. Hansen has a name, Hercules Hansen, and what a name that is, Herc, he tells him_, please_, he says to him.

And the way Mr. Hansen's voice breaks over that single syllable is what clues him in.

There is blood all over the threadbare Henley, grey looking black in smears when Stacker looks back to the shadows where the man is standing there by the stone steps, unmoving but shaking in the wind. He thinks he says something like _sorry for your loss_, but his eyes can already see blood from where he is standing, and he doesn't wonder what this man has come home to.

Stacker excuses himself and walks into the house.

The stench of blood is thick and fresh when he takes that very first step inside. There is the afternoon sun filtering through from the windows at the end of the hall. Looking down, Stacker sees the sight of a dog lying at the threshold, an English bulldog that is all bloodied fur, desecrated and still barely in one piece.

"Overkill," he murmurs, and he doesn't know whether he is talking to himself or someone else altogether, but there's Tendo Choi nodding in agreement as he gestures to the next room.

Stacker makes his round.

There's a woman lying like a crumpled paper doll on the kitchen floor, single bullet wound to the back of her head, a little boy in the living room with the television screen still playing the Saturday cartoons killed in the exact same manner.

Homicides with kids are never easy, like they should never be.

Stacker rubs a hand down his face, his eyes closing, just for a second, because he still has the luxury then. But the splatter of blood across the tiles and the walls from the double homicide of Angela Hansen and young Charles Hansen remains a sight seared bright into his mind.

And when he steps out, for a breath that isn't stinking of the fresh stench of blood, he finds the father still standing outside of the house, falling silently apart.

.

He sits at the table in the interrogation room, head in his hands, and only musters enough strength to lift his head up when Stacker walks through the door with two Styrofoam cups and a file tucked beneath one arm.

"Not the greatest coffee in London, but we get by."

That pulls the thinnest smile out of the man.

"Thank you, detective."

.

It's the way he breaks apart with each question asked, sadness in his eyes when he looks down, ginger lashes fanning across the freckles of his cheeks. Stacker watches his hands clenching and unclenching into fist and palm, wedding ring a bright silver band in the harsh lights of the interrogation room.

It's the way he smiles through the grief he pulls off so well. The way empathy doesn't touch him even when Stacker is doing his damnest to reach out. The tape running its course between them.

"You will slip up."

Hercules blinks. And he looks every bit like the heartbroken father who is still too deep in shock to begin the process of mourning.

Call it intuition, and faith, and experience alone.

"It was you."

Stacker Pentecost knows that Hercules Hansen is the one to pull the trigger.

"Then prove it."

Hercules leans forward and laces his fingers together over the surface of the table.

.

The crime scene photos are spread out across his desk when Tendo walks in with the model of the gun that is a closest match to the ballistics. He disassembles it into its components and lays it down for Stacker to see.

"Lightweight polymer, easy to carry." Tendo tells him, holding up the frame.

"…Polymer burns."

"A lot of things burn, boss."

And everything clicks into place.

.

Stacker finds the gun, proves him wrong and himself right, but only the remaining pieces (carbon steel barrel and springs) that doesn't melt away in the incinerators. It is evidence that will never hold up in court, and _that_ is something they both know.

They are standing on the bridge.

Stacker Pentecost has the dog's ashes in one hand and Hercules Hansen pressing the edge of a kitchen knife into his stomach. He can feel the pressure through his suit, and learns that the man holds a knife just as well as he can hide a gun. (Because whoever thought of putting it in the dog? Reaching down through its esophagus to deposit the dismantled gun in the stomach of the family dog.)

"That's mine." Hercules cocks his head to the side and eyes the urn of Max's ashes Stacker has dangling over the river in warning. The fact that there is a knife to his stomach and the eyes of a sociopath boring into his own only pushes him to curl a smirk over his lips. "Is the gun yours too then?"

"You can't prove it."

"Doesn't matter." Stacker shakes his head and there is a second of recognition in Hercules' eyes. Just as promised though, Stacker just drops the urn into the river. "I found you out."

It's risk, but many things are.

Instead of having the knife going through skin and flesh, Hercules pulls back with a smile that cuts just as deep. He tucks the knife back into his sleeves, slides it against thin shirt and thinner skin. He looks out into the water, murky depth spanning, and he tells him, profile looking like a father that is only beginning to mourn.

"Kid loved that dog."

.

"You need me."

Hercules calls out to him, and it's not on a whim but a perfectly calculated move that he makes, like all the other ones that doesn't include meeting DCI Stacker Pentecost.

Stacker stands still, and Hercules continues.

"Maybe not today, and maybe not tomorrow. But one day, you're going to need me."

He thinks they may be thinking about Tamsin Sevier, and the murder of Luna Pentecost. He thinks they may be thinking of Tamsin still in a coma, and the things she is capable of saying if or when she wakes up from her fall.

"…And what, Hercules? Dial you up?" Stacker turns around, indulges him in ways he knows he shouldn't. And the part of him that has nothing to do with pity or disgust is sparking away because that is interest when he turns around to look at Hercules Hansen. "I don't suppose you will be so easy to reach."

"For you, I might just be that easy." He smiles, and his mouth stretches into something of a poor imitation of what joy might be, like he doesn't even try. That in itself is a surprise all on its own, a statement that goes something like _you see me for who I am so why pretend_. "And please, _Stacks_. Call me Herc."

The name makes him flinch.

The name reminds him of her fiery hair and the last gasp of his name as his sister dies at the hands of a woman she's never loved quite like this one.

.

Hercules Hansen walks.

Because the judicial system is flawed and maybe, there really does exist the perfect crime. For all that the case is wrapped up, the two of them have only begun because Hercules Hansen fixates.

And his fixation consists of the twisted and deranged.

(And on a level Stacker Pentecost doesn't want to understand, he does the same with the man from down under.)

.

"The things I do for you, Stacks."

Herc smiles, and if Stacker has no idea what this man has done, or more so of what he's capable of, well, it could've been a lovely thing. But that isn't the case. In fact, that is never going to be the case.

"I'd rather you didn't."

"Too late."

Herc doesn't show him the hand covered in proverbial blood, he is much too careful for that. Much better than the mess in the photos of another crime scene that Stacker has just been assigned to, one that is almost puzzling until Herc comes along with a smile and a pointed look that directs him just right with questions worded all wrong.

(It isn't that Stacker can't solve a case on his own, it is that it would be a shame to have a man like that fall into the same mindset that is hardwired into Herc's own. Though he does love the way his mouth would pull into a grimace because for all that Hercules fixates on Stacker, he also fixes the man.)

"Can you guess the last thing she said?"

Herc leans in close, mouth close enough to press a kiss to the side of Stacker's cheek. And even without pulling away, Stacker can feel the slow stretch of a smile that seems to wane over his skin. His voice is low and rough, a rasp like the brush of stubbles against Stacker's cheek.

And it goes down smooth when he finally shares Tamsin Sevier's last words.

"_Stacks_."

.

After the mysterious death of Tamsin Sevier, two days after she wakes up from her coma, Stacker Pentecost is entrusted with Mako Mori.

She is twenty-one, a mess, and becomes something of a surrogate daughter, which makes little sense because he's never had one to begin with. He cares for her in ways he's never cared for anyone before.

So, when she is taken, he only knows one man he can turn to.

.

"You're asking me to be your accomplice?"

He is standing in Hercules' apartment at four in the morning, the man barely two feet away from him in nothing but a pair of briefs that hides nothing. Stacker learns that the freckles don't stop at just a scatter over his cheeks but his neck and shoulders and chest and the long line of his back, and then even further down too.

But he deliberately doesn't look _there_, and that in itself makes Herc smile something that is not at all appropriate.

The only sobering thought is that Mako has been missing for 24 hours. He hasn't slept in just as long, and the facts are these: Tendo has no leads, and if she dies, she dies in his name.

There are many things he won't do, but just as many that he will do for her.

Hercules closes that short distance between them, lays a hand across his cheek and angles him so he can't break eye contact.

"Yes." Stacker admits, and it's no small secret to agree to.

"Excellent."

He makes him tea, and it's no good, but Stacker drains the cup and lets the man pull him down on the sofa for just a bit of sleep. There are no breaks to mend or space to hold, just a span of skin that warms where they touch when they finally do.

.

He finds her for him, and kills the men responsible.

Stacker doesn't agree with the way he kills, without hesitation and punishing in ways he has no right to. And he remembers a conversation they've once had, in which Hercules tells him that murder is simple, and guilt and innocence is just that. In which he replies that murder is not the same as an inability to save even when the outcome is the same.

Where the inability to do so is only a simple matter of perspective.

He doesn't kill Tamsin Sevier. But Stacker Pentecost does leave her to die.

Not once, but twice. The second time sticks.

.

"Why'd you do it?"

Hercules makes a soft noise, his hands don't stop from cleaning the gun he used to kill the men holding young Mako Mori in captivity.

"Your wife, and your kid." Stacker says, like Herc has ever needed any clarification.

"…Why do we do anything that we do?" He asks him in return, mouth a soft curve when he tilts his head to the sun. "Hm? Stacker, you're a smart man, I'm sure you can answer that question."

"For anyone else, probably."

Hercules looks to him, raises a brow.

"Yes." Stacker corrects himself, remembering all those brutal murders that he has fixated on, but none even capable of comparison to the one standing next to him. "But for you, you've always been special."

"Special is one way to put what I am into perspective." They are standing by the harbour, Stacker sitting against the hood of his car, Hercules dismantling the gun and wiping away the discriminating prints. "There's quite a positive connotation to that."

And he looks at him like it really doesn't. But that isn't regret or guilt in his eyes, just the acknowledgement that there's something broken in his head, something mended wrong.

"Maybe I'm just living up to my name's sake."

Hercules says as he throws the components into the harbour, and he only turns around to press his lips to his.

.

"I think I might go back home."

Herc starts, and there is a wonder in the way he murmurs that last word, like it's something he's just beginning to wrap his head around. And Stacker won't be surprised to find if that really is the case.

The two of them are standing outside of Mako Mori's hospital room, visiting hours having just ended. The lights are beginning to dim and the young woman is waving at them with a tired smile from behind the glass. There are bandages where there are cuts and pity where there are bruises that sink beneath skin and flesh to bones and marrow and even further in.

"Australia."

"Yeah, Stacks," Hercules waves back at Mako with a half smile, "it's a nice place."

"Warm."

"Very."

He doesn't ask him to come down under with him.

And he, in turn, doesn't say _yes_.

.

Stacker gets a postcard.

Something tacky and ridiculous with kangaroos and koalas. It's no way to keep contact, but it isn't like Stacker has it stuck to his fridge with the robot magnets Mako insists look cute. But well, it isn't like Stacker has thrown it into the trashcan either, and _that_ speaks louder than anything he pretends to say otherwise.

He turns it over, again and again, in his hands.

Mako doesn't point out the local London stamp at the corner of the postcard, doesn't need to. She just leans over the kitchen counter to swipe an apple from the bowl, to ask that same question Stacker himself has been asking since he met the man on that Saturday afternoon.

Where Hercules has been covered in blood, standing in the shades, shaking like a leaf in the wind, and Stacker has been foolish enough to think him as anything but the killer that he is for even a second.

Mako bites into the fruit, and asks.

"So, now what?"

XXX Kuro


End file.
